Encoder Position Accuracy via Multi-Pitch Signal Correction
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Solution Overview
Problem
Existing encoders face challenges in achieving high accuracy due to displacement errors and image magnification errors caused by the relative inclination between the scale and sensor, leading to decreased accuracy in position detection.
Innovation Solution
The encoder employs a configuration with a scale having multiple periodic patterns of different pitches, detected by a light-receiving element array with a signal processing circuit that separates and corrects signals to reduce errors, using a combination of signal acquirers, correction value calculators, and phase calculators to produce accurate position information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple light-receiving element arrays are used to detect periodic patterns in multiple tracks, then position detection capability is enhanced, but mounting position displacement and image magnification errors increase, deteriorating measurement precision
Solution Approach 1:
The scale is divided into multiple tracks, each with periodic patterns of different pitches. Each track is detected by a corresponding light-receiving element array. The signal processing circuit separately processes signals from each track and synthesizes them to achieve high-precision absolute position detection while reducing the impact of mounting errors through the combined information from multiple tracks.
Solution Approach 2:
Periodic patterns with different pitches (spatial frequencies) are used in different tracks. By using patterns with varying periods, the system can detect positions with different resolutions and combine these measurements to achieve high accuracy while being less sensitive to mounting position variations and image magnification errors.
2Measurement precision
If multiple light-receiving element arrays are used to detect periodic patterns in multiple tracks, then position detection capability is enhanced, but device complexity increases
Solution Approach 1:
Multiple light-receiving element arrays are integrated into a single sensor unit with a unified structure. The signal processing circuit combines signals from all tracks and performs synthesis processing to generate absolute position information, reducing the overall complexity compared to using separate detection systems for each track.
Solution Approach 2:
The sensor unit is designed to detect periodic patterns in multiple tracks simultaneously using a single integrated light-receiving element array. This multi-functional sensor can process signals from different tracks with different pitches, achieving high-precision absolute position detection without requiring separate detection systems for each track.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables highly accurate position detection by reducing signal components related to the second pattern's period, resulting in improved precision and accuracy of position measurement.
Implementation Method 1
a sensor which outputs a periodic signal that periodically changes depending on the periodic pattern in response to relative movement of the scale and the sensor
Data Source
Figure 1~2
Figure 3~4
Figure 5~6B
AI summary
The encoder includes a scale (20A, 20B, 20C) provided with first and second periodic patterns, a sensor (10A, 10B) movable relatively with respect to the scale and including a detection element array (16A, 16B) to detect the first and second periodic patterns, a periodic signal producer (40, 41, 42) to produce, by using output from the detection element array, a first periodic signal changing corresponding to a first period of the first periodic pattern and a second periodic signal changing corresponding to a second period of the second periodic pattern, and a correction signal producer (40, 43) to produce, by using the second periodic signal, a correction signal for reducing in the first periodic signal a signal component changing corresponding to the second period. A position calculator (40, 44-46) produces, by using the first periodic signal and the correction signal, information indicating position.